Patches and Corridors in Wildlife Conservation

Fragmented Landscapes

Tropical and temperate landscapes both exhibit a high degree of “patchiness” where forest habitat has been left amid an agricultural matrix characterized by pasture lands, fallows, and annual and/or perennial cropping systems. These fragments serve as habitat and may often represent the last hope for safeguarding species in the area.

The challenge to conservationists—often in the face of rampant development—is how best to manage patches in order to maximize and preserve the wildlife they harbor. For a given species, many or all the patches in a region may contain a local population relatively or totally restricted to that patch. The small, isolated populations dotting a landscape in these patches can be grouped together as a metapopulation, a term coined in 1969 by Richard Levins, a theoretical ecologist who was thinking about agricultural pests at the time.

As island habitats, patches are likened to true ocean islands, adhering to the theoretical principles and processes of island biogeography. Theory predicts that small patches contain and preserve fewer species than larger ones, and more isolated patches experience higher extinction and lower colonization rates than less isolated ones. Yet with several patches in a region, any given species that goes extinct on one “island” can get reestablished via colonization (the “rescue effect”) in other patches—assuming that the organism can get there. Local extinction and recolonization take place within the patches, but the overall meta population survives. This is where the concept of corridors comes into play. Corridors form the pathways connecting these patches, and their creation or preservation and maintenance have been recognized and debated as viable ways to protect populations restricted to patches.

The proposed advantages of corridors include the maintenance of metapopulations, the concomitant maintenance of species diversity, the possibility of a rescue effect for any patch experiencing extinction of a species, and greater genetic variability delivered from the metapopulation. Yet homogenization of the total genetic variability throughout the patches could occur, countering any patch-specific adaptations that might otherwise develop. Moreover, just as species of conservation concern can move between patches, so too can parasites, diseases, and exotic/invasive species. Though theoretical modeling and empirical observations have focused on the role and potential outcome of these biological corridors, the dearth of reliable data means that the benefits and drawbacks of corridors’ true conservation value are debatable.

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